A. Field of Invention
The present invention relates to the field of immunology and hyperproliferative diseases. More particularly, the present invention relates to a method of detecting and monitoring a therapeutic antibody:antigen complex, soluble antigen, free therapeutic antibody and soluble total therapeutic antibody, wherein a patient has undergone at least one dose of immunotherapy. Yet further, the methods may be used to monitor or stage a hyperproliferative disease by measuring the levels of therapeutic antibody:antigen complexes, soluble antigens or soluble therapeutic antibodies.
B. Description of the Related Art
1. Clusters of Differentiation
Clusters of differentiation (CD) have been established to define human leukocyte differentiation antigens (Bernanrd and Boumsell, 1984) by the comparison of reactivities of monoclonal antibodies directed against the differentiation antigens. These cell surface antigens serve as markers of cell lineage and distinguish populations of leukocytes with different functions, e.g., neutrophils and monocytes.
Leukocyte cell surface antigens have enormous clinical application potential for the identification of leukocyte populations and their functional status (Krensky, 1985, Kung et al., 1984; Kung et al., 1983; Cosimi et al., Knowles et al., 1983; and Hoffman, 1984). For example, measuring the total numbers of T cells by surface markers has been useful for the characterization, diagnosis and classification of lymphoid malignancies (Greaves, et al., 1981) and viral infection associated with transplantation (Colvin, R. B et al., 1981), and AIDS (Gupta, 1986; Ebert et al., 1985).
a) CD20
CD20, also called B1 (Bp35), is a cell surface phosphoprotein detected on the surface of B-lymphocytes (Tedder and Schlossman, 1988; Warzynski et al., 1994; Algino et al. 1996). CD20 has a major role in the regulation of human B-cell activation, proliferation and differentiation (Golay et al., 1985; Tedder and Engel, 1994; Kehrl et al., 1994). It has been reported that CD20 is heavily phosphorylated in malignant B-cells and proliferating B-cells when compared to non-proliferating B-cells (Tedder and Schlossman, 1988). Based on sequence analysis, the CD20 molecule appears to have four transmembrane domains with n- and c-terminal domains in the cytoplasm (Kehrl, et al., 1994). The molecule appears to regulate transmembrane Ca++ conductance (Tedder and Engel, 1994). Antibodies directed towards the extracellular portion of CD20 appear to activate a tyrosine kinase pathway that modulates cell cycle progression by interaction with src-related kinases (Deans et al., 1995; Popoff et al. 1998; Hofineister et al., 2000). Relocalization of CD20 into a detergent-insoluble membrane compartment upon binding to antibodies has also been reported (Deans et al., 1998). Several investigators have documented variations in the intensity of CD20 expression on the surface of malignant B-cells in different lymphoproliferative diseases (Almasri et al., 1992; Ginaldi et al., 1998). This is important in view of the success an anti-CD20 monoclonal antibody (Rituximab) in treating various B-cell malignancies (Maloney et al., 1999; Dimopoulous et al., 2000; Zinzani et al., 2000; Hainsworth, 2000; Keating et al., 2000; McLaughlin et al., 2000: Kuehnle et al., 2000). The reported structure of the CD20 molecule suggests that it is not secreted and is highly unlikely to be shed from the cell surface (Riley et al., 2000).
b) CD52
The CD52 antigen is a glycoprotein with a very short mature protein sequence consisting of 12 amino acids, but with a large carbohydrates domain (approximately 3 times the size of the protein domain) (Xia, M. Q. et al., 1993; Treumann, A. et al., 1995). CD52 is expressed on the surface of T- and B-lymphocytes, monocyte/macrophages, eosinophils and some hematopoietic progenitors (Rowan, W. et al., 1998; Elsner, J. et al., 1996; Taylor, M. L. et al., 2000; Gilleece, M. H. et al., 1993). CD52 is also expressed in the male reproductive tract, mainly in the epithelial lining cells of the distal epidermis, vas deferens, and seminal vesicles (Kirchhoff, C. et al., 1995; Kirchhoff, C. et al., 1993; Kirchhoff, C. 1996; Kirchhoff, C. et al., 1997; Kirchhoff, C., 1998; Kirchhoff, C. et al., 2000). CD52 is necessary for spermatozoa to preserve normal motility. It is shed into seminal plasma and then acquired by sperm cells to enable their passage through the genital tract, thus it is detectable on the surface of epididymal sperm and in the ejaculate, but not on either spermatogenetic cells or testicular spermatozoa. The protein core of the sperm and lymphocyte CD52 is identical—both are products of a single copy gene located on chromosome 1(1p36) (Tone, M. et al., 1999). However, N-linked carbohydrate side chains and the GPI-anchor structure are different. The physiological role of CD52 on lymphocytes is unclear.
The Campath-1 family of monoclonal antibodies was originally generated by immunizing rats against human T-cells (Friend, P. J. et al., 1991). Later studies show that Campath-1 antibodies recognize CD52 (Xia, M. Q. et al., 1993; Xia, M. Q. et al., 1991; Hale, G. et al., 1990). Several forms, both IgG and IgM, were generated. The IgG1 form of Campath-1 was humanized and this agent, Campath-1H (Alemtuzumab), has recently been approved for the treatment of refractory chronic lymphocytic leukemia (CLL) Finkelstein, J. B. et al., 2001; Rawstron, A. C. et al., 2001; Riechmann, L. et al., 1988). The Campath-1 family of antibodies is also being used in vitro for lymphocyte depletion in allogeneic marrow grafts and is being investigated as immunomodulatory therapy in a variety of diseases (Moreau, T. et al., 1996; Matteson, E. L. et al., 1995; Lim, S. H. et al., 1993; Lockwood, C. M. et al., 1993; Lockwood, C. M., 1993; Lockwood, C. M. et al., 1996; Dick, A. D. et al., 2000; Hale, G. et al., 2000; Isaacs, J. D. et al., 1992; Lim, S. H. et al., 1993; Mehta, J. et al., 1997; Naparstek, E. et al., 1999; Naparstek, E. et al., 1995; Novitzky, N. et al., 1999; Or, R. et al., 1994).
Antibodies against CD52 are believed to initiate killing of cells through antigen cross-linking (Hale, C. et al., 1996). As a result of this cross-linkage, several cytokines are released including tumor necrosis factor-α, interferon γ and interleukin (Elsner, J. et al., 1996; Wing, M. G. et al., 1996; Wing, M. G. et al., 1995). Cross-linking of CD52 by antibodies promotes apoptosis and antibody-dependent cellular cytotoxicity, which may count for the effectiveness of Campath-1H in treating patients with chronic lymphocytic leukemia (CLL) (Rowan, W. et al., 1998; Rawstron, A. C. et al., 2001; Greenwood, J. et al., 1994; Xia, M. Q., et al., 1993). CD52 is expressed on the surface of neoplastic lymphocytes in patients with CLL, low-grade lymphomas and T-cell malignancies (Dyer, M. J., 1999; Dybjer, A. et al., 2000; Pawson, R. et al., 1997; Salisbury, J. R. et al., 1994; Matutes, E. 1998). Some cases of myeloid, monocytic and acute lymphoblastic leukemia also express CD52 (Belov, L. et al., 2001; Hale, G. et al., 1985). This wide expression of CD52 in a variety of hematological malignancies has led to increasing interest in using Campath-1H in treating these malignancies (Khorana, A. et al., 2001; Keating, M. J. 1999).
CD52 is shed in the male productive system and the soluble molecules play an important role in preserving spermatozoa function (Kirchhoff, C., 1996; Yeung, C. H. et al., 1997; Yeung, C. H. et al., 2001). However, it is not known if CD52 is shed from hematopoietic cells and/or detectable in the circulation of patients with CLL.
c) CD33
CD33 is a member of the siglecs family which bind sialic acid. CD33 is restricted to the myelomonocytic lineage of cells. During maturation of myloid cells, the pluripotent hematopoietic stem cells give rise to progenitor cells that have a diminished self-renewal capacity and a greater degree of differentiation. During this development, normal myeloid cells express cell surface antigens, for example CD33. CD33 is present on maturing normal hematopoietic cells, however, normal hematopoietic stem cells lack this cell surface antigen. In addition to maturing normal hematopoietic cells, CD33 is also present on acute myelocytic leukemia (AML). Thus, this myeloid cell surface maker has become an attractive target for monoclonal antibody targeting. Yet further, anti-CD33 antibodies have also been used to deliver radiation or a cytotoxic agent directly to leukemic cells.
2. Immunoassays
Immunoassays are usually used to measure cell surface antigens. Typically, immunofluorescence using flow cytometry is the immunoassay of choice. However, other immunoassays may be used, for example enzyme linked immunosorbant assays (ELISA). This technique is based upon the special properties of antigen-antibody interactions with simple phase separations to produce powerful assays for detecting biological molecules.
One well-known and highly specific ELISA is a sandwich ELISA. In this assay, the antibody is bound to the solid phase or support, which is then contacted with the sample being tested to extract the antigen from the sample by formation of a binary solid phase antibody:antigen complex. After a suitable incubation period, the solid support is washed to remove the residue of the fluid sample and then contacted with a solution containing a known quantity of labeled antibody.
The methodology and instrumentation for the ELISA is simpler than that for immunofluorescence. Yet further, the ELISA and immunofluorescence assays are completely different assays. ELISA assays measure the protein (antigen) in the plasma/serum, which reflects the entire body. Surface immunofluorescent assays measure an antigen on the surface of individual cells and does not provide information on the amount of cells in the body. Thus, there are advantages in developing an ELISA assay to provide a measurement of the entire body.